Polishing pad and method of fabricating semiconductor device

ABSTRACT

A polishing pad includes a first pad portion and a second pad portion disposed therearound, and each of the first and second pad portions is replaced individually. A CMP apparatus with the polishing pad (first and second pad portions) attached thereto conducts polishing of a semiconductor wafer. The second pad portion is replaced with a replacement second pad portion when the total polishing time reaches a predetermined period of time.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims and the benefit of priority of the prior Japanese Patent Application No. 2011-019441, filed on Feb. 1, 2011, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a polishing pad and a method of fabricating a semiconductor device.

BACKGROUND

In the fabrication of a semiconductor device, a chemical mechanical polishing (CMP) apparatus is used in various steps. The CMP apparatus includes: a platen (surface plate) to which a polishing pad (abrasive cloth) is attached; a polishing head which sucks and carries a semiconductor wafer (hereinafter, simply referred to as “wafer”); and a slurry nozzle from which slurry (abrasive) is dripped onto the polishing pad. The CMP apparatus polishes the surface of the wafer by dripping slurry onto the polishing pad, pressing the polishing pad against the wafer, and rotating one or both of the platen and the polishing head.

Meanwhile, conducting this CMP for a long period of time causes the adhesion of polished debris to the polishing pad and the like and changes the surface condition of the polishing pad, making uniform polishing impossible. For this reason, the surface of the polishing pad is ground by use of a tool called a conditioner to restore the surface condition after the CMP is conducted for a predetermined period of time, for example. This treatment to restore the surface condition is called conditioning.

Patent Literature 1: Japanese Laid-open Patent Publication No. 08-264497

The conditioning is an important work for conducting stable polishing. However, frequent conditioning shortens the life of the polishing pad and therefore increases the fabrication cost of a semiconductor device.

SUMMARY

According to an aspect of the disclosed technique, there is provided a polishing pad of a polishing apparatus including: a first pad portion; and a second pad portion disposed around the first pad portion and being separable from the first pad portion.

The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram for describing the configuration of a general CMP apparatus;

FIG. 2 is a schematic diagram for describing behaviors of the CMP apparatus;

FIG. 3 is a graph illustrating the result of investigation of the correlation between the total conditioning time and the distribution of the thickness of a polishing pad in the in-plane direction thereof;

FIG. 4 is a graph illustrating the thickness distribution of a new polishing pad and of a polishing pad on which conditioning is conducted until grooves in its outer peripheral portion are worn away;

FIG. 5 is a graph illustrating the in-plane polishing-rate profile of a wafer obtained when the total conditioning time is 1.8 hours and 7 hours;

FIG. 6 is a graph illustrating the result of measurement of the thickness distribution of a polishing pad taken when the total conditioning time is 1.8 hours and 6.8 hours;

FIG. 7A is a plan view for describing a polishing pad according to a first embodiment, FIG. 7B is a plan view illustrating a state where a first pad portion and a second pad portion are separated from each other, and FIG. 7C is a cross-sectional view of the same polishing pad;

FIG. 8 is a flowchart describing an example of a method of determining the timing to replace the second pad portion and the thickness of a new second pad portion for replacement;

FIGS. 9A to 9C are diagrams illustrating procedures for replacing the first and second pad portions;

FIG. 10 is a flowchart for describing a method of fabricating a semiconductor device by using the polishing pad according to the first embodiment;

FIG. 11 is a graph illustrating the thickness distribution of a polishing pad in a brand-new state;

FIG. 12 is a graph illustrating the thickness distribution of the polishing pad having reached a replacement timing X for its second pad portion;

FIG. 13 is a graph illustrating the thickness distribution of the polishing pad after its second pad portion is replaced; and

FIG. 14A is a plan view for describing a polishing pad according to a second embodiment, and FIG. 14B is a plan view illustrating a state where a first pad portion and a second pad portion are separated from each other.

DESCRIPTION OF EMBODIMENTS

Before describing embodiments, a prelude will be described below to facilitate understanding of the embodiments.

FIG. 1 is a diagram for describing the configuration of a general CMP apparatus.

A general CMP apparatus is provided with a plurality (three in FIG. 1) of platens 10 on a base 2, and one load cup 20. The platens 10 and the load cup 20 are disposed around a revolving shaft 30 a.

Each platen 10 has a polishing pad mounted thereon. Moreover, each platen 10 has a slurry supply arm 31 and a conditioning-disk drive arm 32 (conditioner) disposed therearound. The slurry supply arm 31 is provided with a slurry supply nozzle at the leading end thereof. The conditioning-disk drive arm 32 has a conditioning disk 12 attached thereto.

The load cup 20 is provided with a pedestal (sample stage) and a water-washing nozzle (unillustrated) therein. The pedestal temporarily holds an unpolished or polished wafer. The water-washing nozzle is used to wash the wafer and the pedestal.

Above the base 2, there is disposed a head unit 30 which is supported on and revolves around the revolving shaft 30 a. This head unit 30 is provided with polishing heads 14 on its lower side. The number of the polishing heads 14 is equal to the total number of the plates 10 and the load cup 20 (four in FIG. 1). Each polishing head 14 rotates along with the rotation of its rotation shaft 14 a. The rotation shaft 14 a also reciprocates in directions indicated by arrows in FIG. 1 (the radial direction of the revolving movement of the head unit 30).

Each polishing head 14 is provided with a rubber membrane 16 in the form of a thin film on its lower side. By driving this membrane 16 with use of an air-pressure adjustment mechanism (unillustrated), the polishing head 14 may suck or release a wafer. Moreover, the head unit 30 revolves with the polishing heads 14 sucking wafers to carry the wafers onto the platens 10.

FIG. 2 is a schematic diagram for describing behaviors of the CMP apparatus. In FIG. 2, reference signs 10 a, 12 a and 13 denote the rotation shaft of the platen 10, the rotation shaft of the conditioning disk 12, and a wafer to be polished, respectively.

As illustrated in FIG. 2, a polishing pad 11 is mounted on the platen 10. Moreover, a slurry supply nozzle 15 is provided at a leading end portion of the aforementioned slurry supply arm 31. This slurry supply nozzle 15 is connected to a slurry supply apparatus (unillustrated) via a slurry supply tube 15 a, and slurry is dripped from the slurry supply nozzle 15 onto the polishing pad 11.

When the CMP apparatus polishes the wafer 13, the slurry is first dripped from the slurry supply nozzle 15. Then, the polishing head 14 is caused to hold the wafer 13. Thereafter, with the platen 10 and the polishing head 14 being rotated, the polishing surface of the wafer 13 is brought into contact with the polishing pad 11.

The slurry dripped onto the polishing pad 11 is supplied between the polishing pad 11 and the wafer 13 by the rotation of the platen 10. As a result, the surface of the wafer 13 is polished mechanically and chemically by the polishing pad 11 and the slurry.

Meanwhile, the polishing pad 11 is provided with grooves of a concentric, spiral, or grid pattern in its surface. The slurry dripped onto the polishing pad 11 is supplied to the surface of the wafer 13 mainly through these grooves in the polishing pad 11. Moreover, the slurry after used in the polishing is released from the surface of the wafer 13 mainly through the grooves in the polishing pad 11 as well.

If the grooves in the surface of the polishing pad 11 are worn away, sufficient slurry may not be supplied to the wafer 13. Insufficient slurry lowers the polishing rate or makes the uniform polishing of the whole surface of the wafer impossible. Insufficient slurry may also be a cause of the slip-out of the wafer 13 from the polishing head 14 during the polishing. Thus, it is important to replace the polishing pad 11 before the grooves are worn away.

FIG. 3 is a graph illustrating the result of investigation of the correlation between the total conditioning time (the sum of times spent for conditioning) and the distribution of the thickness (thickness profile) of a polishing pad in the in-plane direction thereof. The horizontal axis represents the distance from the center of the polishing pad whereas the vertical axis represents the thickness of the polishing pad. Note that in the following description, the thickness of the polishing pad refers to the thickness of the abrasive layer of the polishing pad (i.e. excluding the thickness of the base layer).

As illustrated in FIG. 3, conducting conditioning does not decrease the thickness of the polishing pad uniformly; there are variations in the decrease. Specifically, as compared to a center portion of the polishing pad, the thickness decreases greatly in a peripheral portion.

Meanwhile, it may be possible to adjust the thickness distribution of the polishing pad by adjusting the condition on which conditioning is conducted. However, adjusting this conditioning condition to achieve a uniform thickness of the polishing pad is difficult and time-consuming and therefore causes increase in the fabrication cost of a semiconductor device. Alternatively, the thickness distribution of the polishing pad is made ununiform purposely to achieve a desired polishing rate in some cases.

FIG. 4 is a graph illustrating the thickness distribution (thickness profile) of a new polishing pad and of a polishing pad on which conditioning is conducted until the grooves in its outer peripheral portion are worn away. The horizontal axis represents the distance from the center of each polishing pad whereas the vertical axis represents the thickness of the polishing pad. Note that the total conditioning time is 0 minute for the new polishing pad and 400 minutes for the polishing pad on which conditioning is conducted until the grooves in its outer peripheral portion are worn away.

As seen from FIG. 4, even after conducting conditioning until the grooves in the outer peripheral portion are worn away, grooves with sufficient depths still exist in a center portion of the polishing pad.

FIG. 5 is a graph illustrating the in-plane polishing-rate profile of a wafer obtained when the total conditioning time is 1.8 hours and 7 hours. The horizontal axis represents the distance from the wafer center whereas the vertical axis represents the polishing rate.

Here, a wafer having a tetra ethoxy silane (TEOS) film formed on its surface and having a diameter of 300 mm is used as the polishing sample, and a polishing rate is calculated which is based on CMP performed on the sample surface for 120 seconds after the elapse of a total conditioning time of 1.8 hours and after the elapse of a total conditioning time of 7 hours. Moreover, a polishing pad having a diameter of 77.5 cm and having a base layer made of a non-woven fabric and an abrasive layer made of urethane foam is used here. Further, as the conditioning disk, a commercially available conditioning disk is used in which diamond of a size of 100 mesh is electrodeposited in a spot (circular) shape on a stainless-steel washer by means of nickel (Ni) plating. Furthermore, as the slurry, a slurry is used which is obtained by dissolving colloidal silica in pure water and adding an organic acid and aqueous hydrogen peroxide thereto.

The polishing condition is listed in Table 1 below. Note that Retaining Ring in Table 1 refers to a pressure applied to a retaining ring provided to an outer peripheral portion of the polishing head. Zones 1 to 3 in Table 1 refer to pressures applied respectively to three regions (zones 1 to 3) of the wafer defined by dividing the wafer on the basis of mutually different distances from the wafer center.

TABLE 1 Pressure (g/cm²) Retaining Ring Zone 1 Zone 2 zone 3 500 260 150 200 Slurry Flow Rate Platen Rotation Head Rotation (ml/min) Number (rpm) Number (rpm) 300 65 68

A desired polishing-rate profile illustrated in FIG. 5 is obtained when the total conditioning time is 1.8 hours. On the other hand, when the total conditioning time is 7 hours, the polishing-rate profile is significantly different from that obtained when the total conditioning time is 1.8 hours, despite that the CMP is performed on the same polishing condition.

Specifically, the polishing rate in an outer peripheral portion of the wafer indicates a large decrease when the total conditioning time is 7 hours as compared to when the total conditioning time is 1.8 hours. The polishing rate in a region covering an approximately 125-mm range from the wafer center indicates a decrease as well. However, the polishing rate in a position approximately 130 mm away from the wafer center is substantially the same as when the total conditioning time is 1.8.

In the case of FIG. 5, when the total conditioning time is 1.8 hours, a standard deviation σ of the polishing rates is equal to 3.94%, and the difference between the greatest and smallest values of the polishing rates is 14.1 nm/min. Moreover, when the total conditioning time is 7 hours, the standard deviation σ of the polishing rates is equal to 6.91%, and the difference between the greatest and smallest values of the polishing rates is 28.4 nm/min.

Being unable to measure the thickness of the polishing pad used in the above occasion, we use a new polishing pad and measure the thickness distribution (thickness profile) of this polishing pad when the total conditioning time is 1.8 hours and approximately 7 hours (6.8 hours). The result is illustrated in FIG. 6. Note that in the measurement of the thickness of the polishing pad, the abrasive layer (resin layer) of the polishing pad is removed from the base layer (non-woven fabric) thereof, and the thickness of the abrasive layer is measured by use of a micrometer. The conditioning condition is listed in Table 2 below.

TABLE 2 Conditioning Conditioning Platen Rotation Disk Rotation Pressure (kgf) Time (sec) Number (rpm) Number (rpm) 4 25 83 86

As seen from FIG. 6, a region covering an approximately 30-cm range from the center of the polishing pad indicates small variations in thickness in both cases where the total conditioning time is 1.7 hours and 6.8 hours. On the other hand, while a peripheral portion of the polishing pad indicates a relatively small decrease in thickness when the total conditioning time is 1.7 hours, the peripheral portion of the polishing pad indicates a large decrease in thickness when the total conditioning time is 6.8 hours.

From FIGS. 5 and 6, it is assumed that a cause of failing to obtain a desired polishing profile when the total conditioning time is 6.8 hours is the large difference in the thickness of the polishing pad between the center portion and peripheral portion of the polishing pad.

Hereinbelow, embodiments will be described by referring to accompanying drawings.

First Embodiment

FIG. 7A is a plan view for describing a polishing pad according to a first embodiment, FIG. 7B is a plan view illustrating a state where a first pad portion and a second pad portion are separated from each other, and FIG. 7C is a cross-sectional view of the same polishing pad.

As illustrated in FIGS. 7A to 7C, a polishing pad 40 of this embodiment is divided into a circular first pad portion 40 a and an annular second pad portion 40 b disposed surrounding this first pad portion 40 a. In addition, each of the first and second pad portions 40 a and 40 b has a two-layer structure including a base layer 41 a and an abrasive layer 41 b disposed thereon. The base layer 41 a is made of a non-woven fabric, a soft resin, or the like, for example. The abrasive layer 41 b is made of a hard resin, for example.

The abrasive layer 41 b is provided with grooves 42 in its surface. Each groove 42 has a width of approximately 0.4 mm and a depth of approximately 0.38 mm, for example. Although FIGS. 7A and 7B illustrate an instance where the grooves 42 are formed in a grid pattern, the grooves 42 may be formed in a concentric, spiral, or the like pattern. Moreover, instead of or in addition to the grooves, the abrasive layer 41 b may be provided with holes having a diameter of about 1 mm to 5 mm, for example.

In the instance of each of FIGS. 4 and 6, for example, grooves with sufficient depths are still available in an approximately 30-cm range from the center of the polishing pad even when the grooves in a peripheral portion of the polishing pad are worn away as a result of using it for a long period of time. In view of the above instance, in this embodiment, the radius of the first pad portion 40 a is set to 30 cm, and the internal and external radii of the second pad portion 40 b are set to 30 cm and 38.75 cm, respectively. Then, when the depths of the grooves in the second pad portion 40 b become small, the second pad portion 40 b is replaced. In this way, the life of the polishing pad 40 may be extended.

Meanwhile, the first pad portion 40 a is thinner than when it was new, by the time the second pad portion 40 b is replaced. Thus, it is important that a new second pad portion 40 b for replacement (hereinafter, referred to as “replacement second pad portion”) have the same thickness as the thickness of the first pad portion 40 a at the moment of the replacement.

However, it is difficult to measure the thickness of the first pad portion 40 a at the time of replacing the second pad portion 40 b and to adjust the thickness of the replacement second pad portion 40 b to the measured thickness. In light of this, in this embodiment, the correlation between the total conditioning time and the groove depth is figured out in advance, and the timing to replace the second pad portion 40 b and the thickness of the replacement second pad portion are determined by utilizing the correlation.

A method of determining these will be described below by referring to the flowchart in FIG. 8 and the explanatory diagrams in FIGS. 9A to 9C. In the following, the replacement second pad portion will be denoted by reference sign 40 c for the sake of convenience in description.

First, in step S11, on the platen 10 of the CMP apparatus (see FIG. 1), a new polishing pad 40 (first and second pad portions 40 a and 40 b) is mounted (pasted) (see FIG. 9A). Here, the thickness of the new polishing pad 40 is A.

Next, the process proceeds to step S12, where polishing (CMP) of a wafer and conditioning of the polishing pad 40 are conducted until the polished state of the wafer becomes poor, by using a condition employed in the actual wafer polishing. Then, in step S13, a replacement timing X for the second pad portion 40 b is determined based on the polished state of the wafer subjected to the CMP conducted in step S12.

Next, the process proceeds to step S14, where a new polishing pad 40 (first and second pad portions 40 a and 40 b) is mounted on the platen 10 of the CMP apparatus (see FIG. 9A). Then, the process proceeds to step S15, where the polishing (CMP) of a wafer and the conditioning of the polishing pad 40 are conducted until the replacement timing X by using the condition employed in the actual wafer polishing.

Thereafter, the process proceeds to step S16, where the first pad portion 40 a is taken out, the thickness thereof is measured, and the thickness of the replacement second pad portion 40 c is determined based on the measurement result. Here, we assume that the thickness of the first pad portion 40 a at the replacement timing X is B. So, in this case, the thickness of the replacement second pad portion 40 c is B.

Next, the process proceeds to step S17, where a new polishing pad 40 (first and second pad portions 40 a and 40 b) is mounted on the platen 10 of the CMP apparatus (see FIG. 9A). Then, in step S18, the polishing (CMP) of a wafer and the conditioning of the polishing pad 40 are conducted until the replacement timing X by using the condition employed in the actual wafer polishing.

Next, the process proceeds to step S19, where the second pad portion 40 b is taken out and the first pad portion 40 a is left mounted (see FIG. 9B). Then, a replacement second pad portion 40 c with a thickness of B is mounted on the platen 10 of the CMP apparatus (see FIG. 9C).

Next, the process proceeds to step S20, where the polishing (CMP) of a wafer and the conditioning of the polishing pad 40 are conducted until the polished state of the wafer becomes poor. Thereafter, in step S21, a replacement timing Y for the polishing pad 40 (first pad portion 40 a and replacement second pad portion 40 c) is determined based on the polished state of the wafer subjected to the CMP conducted in step S20.

The actual wafer polishing is conducted once the replacement timing X for the second pad portion 40 b and the replacement timing Y for both the first and second pad portions 40 a and 40 c are determined as described above.

FIG. 10 is a flowchart for describing a method of fabricating a semiconductor device by using the polishing pad according to the first embodiment. The method will be described here by referring also to FIGS. 9A to 9C again as needed.

First, in step S31, a new polishing pad 40 (first and second pad portions 40 a and 40 b) is mounted on each platen of the CMP apparatus (see FIG. 9A). Thereafter, the process proceeds to step S32, where the polishing (CMP) of each wafer and the conditioning of each polishing pad 40 are conducted.

In the next step S33, it is judged whether or not the replacement timing X for the second pad portion 40 b has come. This judgment may be made for example by timing the total polishing time with use of a timing unit (timer) and allowing the operator to make judgment on the basis of the timing result. In addition, the timing unit may be configured to generate alarm whenever the total polishing time reaches the replacement timing X.

If it is judged in step S33 that the replacement timing X has not come yet (NO), the process returns to step S32 to continue the polishing (CMP) of the wafer and the conditioning of the polishing pad 40. On the other hand, if it is judged in step S33 that the replacement timing X has come (YES), the process proceeds to step S34.

In step S34, the second pad portion 40 b is taken out from the platen (see FIG. 9B), and a replacement second pad portion 40 c is mounted as a replacement (see FIG. 9C). Thereafter, the process proceeds to step S35, where the polishing (CMP) of the wafer and the conditioning of the polishing pad 40 are conducted.

In the next step S36, it is judged whether or not the replacement timing Y for the first and second pad portions 40 a and 40 c has come. If it is judged in step S36 that the replacement timing Y has not come yet (NO), the process returns to step S35 to continue the polishing (CMP) of the wafer and the conditioning of the polishing pad 40. On the other hand, if it is judged in step S36 that the replacement timing Y has come (YES), the process proceeds to step S37.

In step S37, the polishing pad 40 (first and second pad portions 40 a and 40 c) is taken out from the platen 10. Then, the process returns to step S31, and the aforementioned steps are repeated.

FIGS. 11 to 13 illustrate changes in the thickness distribution of a polishing pad. FIG. 11 illustrates the thickness distribution of a polishing pad in a brand-new state. FIG. 12 illustrates the thickness distribution of the polishing pad having reached the replacement timing X. FIG. 13 illustrates the thickness distribution of the polishing pad after its second pad portion is replaced.

In this instance, the thickness A of the polishing pad 40 (first and second pad portions 40 a and 40 b) in the brand-new state (FIG. 11) is approximately 1.32 mm. Moreover, the thickness B of the polishing pad 40 (first and second pad portions 40 a and 40 c) after the second pad portion 40 b is replaced with the second pad portion 40 c is approximately 1.04 mm.

In this embodiment, as described above, the polishing pad 40 is divided into the first pad portion 40 a disposed inside and the second pad portion 40 b disposed outside, and each of the first and second pad portions 40 a and 40 b may be replaced individually, perhaps making it possible to replace a worn pad portion. Accordingly, the fabrication cost of the semiconductor device is reduced. Moreover, the amount of polishing pads to be discarded is reduced, and therefore the environmental load is small.

In the foregoing embodiment, a case where the polishing pad 40 is divided into two pad portions (first and second pad portions) is described. Note, however, that the polishing pad 40 may be divided into three or more pad portions.

Moreover, in the foregoing embodiment, a case where the first pad portion is replaced once while the second pad portion is replaced twice is described. However, the first pad portion may be replaced once while the second pad portion is replaced three times, for example. In this case, three types of second pad portions having mutually different thicknesses shall be prepared.

Second Embodiment

FIG. 14A is a plan view for describing a polishing pad according to a second embodiment, and FIG. 14B is a plan view illustrating a state where a first pad portion and a second pad portion are separated from each other.

In the first embodiment, a case where the first pad portion 40 a is circular and the second pad portions 40 b and 40 c are annular is described. However, in the second embodiment, as illustrated in FIGS. 14A and 14B, the first pad portion 40 a is provided with protruding portions 43 a on its outer periphery, and the second pad portion 40 b is provided with recessed portions 43 b in its inner periphery.

As mentioned above, polishing pads are usually provided with grooves of a concentric, spiral, or grid pattern in its surface, and the polishing pad 40 of this embodiment is likewise provided with such grooves in its surface. In a case of a concentric groove pattern, there may be no need to concern the angle (rotation angle in the circumferential direction) between first and second pad portions 40 a and 40 b at the time of disposing the second pad portion 40 b on the outer side of the first pad portion 40 a. In a case of spiral or grid groove pattern, however, it is important to align the grooves in the first pad portion 40 a and the grooves in the second pad portion 40 b with each other.

As illustrated in FIGS. 14A and 14B, the polishing pad 40 of this embodiment is such that the first pad portion 40 a is provided with the protruding portions 43 a and that the second pad portion 40 b is provided with the recessed portions 43 b. Thus, the grooves in the first pad portion 40 a and the grooves in the second pad portion 40 b may be easily aligned with each other by fitting the protruding portions 43 a of the first pad portion 40 a into the recessed portions 43 b of the second pad portion 40 b, respectively.

In this embodiment, the first pad portion 40 a is provided with the protruding portions 43 a, and the second pad portion 40 b is provided with the recessed portions 43 b. Note, however, that the first pad portion 40 a may be provided with recessed portions, and the second pad portion 40 b may be provided with protruding portions. Alternatively, each of the first and second pad portions 40 a and 40 b may be provided with both recessed portions and protruding portions.

All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention. 

1. A polishing pad of a polishing apparatus comprising: a first pad portion; and a second pad portion disposed around the first pad portion and being separable from the first pad portion.
 2. The polishing pad of a polishing apparatus according to claim 1, wherein the first pad portion has a circular shape, and the second pad portion has an annular shape.
 3. The polishing pad of a polishing apparatus according to claim 1, wherein the first pad portion is provided with any one of a protruding portion and a recessed portion in a periphery thereof, and the second pad portion is provided with any one of a recessed portion and a protruding portion in an inner periphery thereof, the recessed portion and the protruding portion of the second pad portion being configured to fit to the protruding portion and the recessed portion of the first pad portion, respectively.
 4. The polishing pad of a polishing apparatus according to claim 1, wherein each of the first pad portion and the second pad portion is provided with a groove in a surface thereof.
 5. The polishing pad of a polishing apparatus according to claim 1, wherein each of the first pad portion and the second pad portion is provided with a hole in a surface thereof.
 6. The polishing pad of a polishing apparatus according to claim 1, further comprising one or more pad portions disposed around the second pad portion and being separable from the first pad portion and the second pad portion.
 7. A method of fabricating a semiconductor device, the method comprising: using a polishing pad separable into a first pad portion and a second pad portion to polish a surface of a semiconductor wafer by pressing the polishing pad against the semiconductor wafer; performing conditioning on a surface of the polishing pad; and replacing any one of the first pad portion and the second pad portion of the polishing pad.
 8. The method of fabricating a semiconductor device according to claim 7, wherein a slurry is supplied onto the polishing pad in the polishing the surface of the semiconductor wafer.
 9. The method of fabricating a semiconductor device according to claim 7, wherein the second pad portion is replaced when a total conditioning time reaches a predetermined period of time.
 10. The method of fabricating a semiconductor device according to claim 9, wherein a thickness of a replacement second pad portion is set based on a thickness of the first pad portion at a moment of the replacement of the second pad portion. 